This invention relates to a lid which is counterweighted to make it easy to open. This invention particularly relates to an access lid for a sub-surface container provided with a counterweight mechanism that is easy to maintain and repair and requires only a minimum amount of space in the container but allows the lid to be opened easily to a fully upright position.
Lids provided with counterweight mechanisms to make them easier to open are well known. See, for example, U.S. Pat. Nos. 402,932, 762,741 and 1,115,554. Especially designed counter weight mechanisms for the heavy access lids of sub-surface containers, such as pits designed for use in servicing aircraft, are also well known. See, for example, U.S. Pat. No. 4,467,932. However, numerous problems have been encountered with such counterweight mechanisms. For example, such mechanisms have typically required relatively large amounts of space for their connections to their lids and for the travel of their counterweights when opening and closing their lids. This has often made it impractical to use such mechanisms in crowded sub-surface containers where space has been at a premium. Such counterweight mechanisms have also typically had to be connected to their lids using relatively complicated mechanical means (e.g., meshed gearing). This has often made such mechanisms difficult to maintain and repair when they have been used in sub-surface containers exposed to harsh environments and to substantial amounts of dirt and grit that can damage their mechanical connections to their lids.
There has been a need, therefore, for a simple counterweight mechanism for an access lid for a sub-surface container which requires only a minimum amount of space and is easy to maintain and repair.